1. Field of the Invention
This invention relates to a binarizing circuit of scanner read image signals.
2. Description of the Related Art
According to the prior art shown in FIG. 4, a scanner 2 reads an image 6 drawn on a paper sheet 4. In order to change the read analog image signals (multi-value voltages) obtained by a sensor reader 2a of the scanner 2 to binary data, a voltage threshold is set and each analog image signal is binarized using the voltage threshold as a boundary. As shown in FIG. 5, a single threshold value T is used in the conventional technology.
As also shown in FIG. 5, if the density of dirt and dust present on the sheet 4 is darker than that of the image 6 (line) to be read, the dirt and dust may also be read, thus producing erroneous results.
More specifically, as shown in FIG. 4, the sensor reader 2a is made up of a plurality of sensors arranged in a line direction. Referring to FIG. 4, assume that one of the plurality of sensors (i.e. sensor 40) detects the presence of the line 6 on the sheet 4 and another of the plurality of sensors (i.e. sensor 100) detects the presence of dust on the sheet 4. The remaining sensor elements detect neither the line 6 nor dirt or dust. As shown in FIG. 5, the output from the sensor element 40 will fall below the threshold T due to the presence of the line 6. Also, the output of the sensor element 100 will fall below the threshold T due to the presence of dust on the paper 4. Thus, the binarized output for the sensor elements 40 and 100 will be zero (BLACK) whereas the binarized output of the remaining sensor elements will be one (WHITE). Thus, since the binarized output for the sensor 100 is zero (denoting "black"), an error in the read operation is created.
It is a purpose of the present invention to provide a binarizing circuit of scanner read images signals which overcomes the shortcomings of the conventional technology.